The algorithm of H∞mixed sensitivity control is summarized and is applied to the vibration control of high order flexible structures, and a method for the choice of the mixed sensitivity weighting matrix is put forward. The algorithm can make the control output signals converge to the reference ones quickly and stably. A multi-input multi-output（MIMO） tracking control model of a vibration system is established via the H∞control theory and the mixed sensitivity design method is used to design the robust H∞ controller.An augment plant for the vibration system is presented by introducing the perfo rmance weighting function matrix and the controlled signal weighting function matrix, including model uncertainties. A MIMO control model with two inputs and two outputs is set up by a cantilever beam. Results show that the control ler for the high order flexible structure can meet the requirements of the internal stability of the control system and the tracking specifications.